Transport accounts for between a quarter and a third of primary energy use in developed economies, and currently this comes almost entirely from liquid hydrocarbon fuels. Anticipating a world with much more expensive oil and a need to dramatically reduce carbon dioxide emissions, many people have been promoting the idea of a hydrogen economy, in which hydrogen, generated in ways that minimise CO2 emissions, is used as a carrier of energy for transportation purposes. Despite its superficial attractiveness, and high profile political support, the hydrogen economy has many barriers to overcome before it becomes technically and economically feasible. Perhaps most pressing of these difficulties is the question of how this light, low energy density gas can be stored and transported. An entirely new pipeline infrastructure would be needed to move the hydrogen from the factories where it is made to filling stations, and, perhaps even more pressingly, new technologies for storing hydrogen in vehicles will need to be developed. Early hopes that nanotechnology would provide new and cost-effective solutions to these problems – for example, using carbon nanotubes to store hydrogen – don’t seem to be bearing fruit so far. Since using a gas as an energy carrier causes such problems, why don’t we stick with a flammable liquid? One very attractive candidate is methanol, whose benefits have been enthusiastically promoted by George Olah, a Nobel prize winning chemist from the University of Southern California, whose book Beyond Oil and Gas: The Methanol Economy
The advantage of methanol as a fuel is that it is entirely compatible with the existing infrastructure for distributing and using gasoline; pipes, pumps and tanks would simply need some gaskets changed to switch over to the new fuel. Methanol is an excellent fuel for internal combustion engines; even the most hardened petrol-head should be convinced by the performance figures of a recently launched methanol powered Lotus Exige. However, in the future, greater fuel efficiency might be possible using direct methanol fuel cells if that technology can be improved.
Currently methanol is made from natural gas, but in principle it should be possible to make it economically by reacting carbon dioxide with hydrogen. Given a clean source of energy to make hydrogen (Olah is an evangelist for nuclear power, but if the scaling problems for solar energy were solved that would work too), one could recycle the carbon dioxide from fossil fuel power stations, in effective getting one more pass of energy out of it before releasing it into the atmosphere. Ultimately, it should be possible to extract carbon dioxide directly from the atmosphere, achieving in this way an almost completely carbon-neutral energy cycle. In addition to its use as a transportation fuel, it is also possible to use methanol as a feedstock for the petrochemical industry. In this way we could, in effect, convert atmospheric carbon dioxide into plastic.
Very interesting…clean up the fuel combustion products with the fuel itself! I guess in the end, we will still need hydrogen production in large quantities from a green source. From all the possible energy choices for the future, and everybody trying to push their own ideas, I wonder is this is preventing progress… this methanol economy certainly sounds nice though.
Since using flammable liquid as an energy carrier causes CO2, why don’t we stick with a solid state battery? Flammable liquid was good when we didn’t know about nanotechnology.
MQ, your point is an entirely fair one in principle; the only difficulty is that the prices and performances of batteries are not improving very fast, so that at the moment battery powered cars don’t really make economic sense. This may change, of course, but the attraction of the methanol economy idea is that it takes into account the substantial inertia of existing technological systems.
Eric, of course you are right, this still doesn’t take away the need to make a lot of either electricity or hydrogen sustainably. Unless, of course, one works out how to make methanol directly from carbon dioxide and water, powered by light energy from the sun. This is certainly possible in principle, but we would need lots of work to find suitable photocatalytic systems.
Once you’re at the stage of synthesizing fuel from CO2 and water, why not make liquid hydrocarbons themselves?
…and then by trying to take advantage of a horseshoe he forgot to create the internal combustion engine…
You could make olefins too, but there wouldn’t really be any point to do this for fuel, as methanol has many advantages as a fuel over gasoline. For diesel engines, you’d use dimethyl ether, a simply made derivative of methanol.
Methanol is the simpest alcohol and as such is the simplest to synthesize. More complex hydrocarbons can be made from the methanol – using a Fischer-Tropsch process – but each step removes energy from the total and the final gasoline is not capable of delivering the same very high levels of thermal efficiency that methanol can give (be better than diesel with the right engine modifications). So, to make higher hydrocarbons from the methanol would (a) deliver less usable fuel energy to the market, (b) give less usable energy on its conversion in the vehicle and (c) require further capital investment in a bigger chemical plant, i.e. well-to-wheels efficiency and economics are both against it. Having said this, it is very important to note that some of the methanol (if made from atmospheric or recovered CO2) should be turned into olefins for plastics etc., because doing this would actually sequestrate what was previously CO2 in a solid form. One can then influence the level of atmospheric CO2 directly. The molecular hydrogen economy cannot allow this – it’s ‘advantage’ of no carbon in the fuel actually becomes its Achilles heel.
Thanks Jamie, you put that more clearly and with more authority than I could.
Whoops, didn’t check back for a while.
Okay. I’d thought gasoline or diesel was actually superior, at least in energy density, vs. alcohols which have oxygen atoms in them taking up mass, but that’s an ill-informed opinion, and certainly energy loss from multiple stages is an obvious consideration.
This is actually one of the few blogs that I want to keep up with.
What is the amount of energy required to convert CO2 into Methanol?
David, I don’t have the figure to hand, but I think that the energetics of the process are dominated by the energy you need to make molecular hydrogen from whatever feedstock you are using; then I think the reaction between CO2 and H2 is exothermic.